Oil, gas, water, geothermal wells and the like are typically drilled with a drill bit connected to a hollow drill string that is inserted into a well casing cemented in a well bore. The drill string includes a plurality of end-to-end connected sections of drill pipe. A drilling head (i.e., a rotating control device) is attached to the well casing, wellhead or to associated blowout preventor equipment, for the purposes of sealing the interior of the well bore from the surface and facilitating forced circulation of drilling substances through the well while drilling or diverting drilling substances away from the well. The drill string passes through the drilling head. Drilling substances include, but are not limited to, water, steam, drilling muds, air, and other flowable substances (i.e., liquids, gases, etc) useful in the drilling operation.
Drilling heads typically include a stationary body, often referred to as a bowl, which carries a bearing assembly. An outer barrel of the bearing assembly is fixedly engaged with the bowl and an inner barrel of the bearing assembly rotates with respect to the outer barrel. The inner barrel of the bearing assembly carries a stripper rubber. The drill string (or other related structure or device) passes through a central bore of the inner barrel and a central aperture of the stripper rubber. A drill bit (i.e., a drill head) is attached to the free end of the last section of drill pipe below the bearing assembly (i.e., the down-hole end of the drill string). In passing through the central aperture of the stripper rubber, the stripper rubber is configured to compressibly and resiliently seals around a outside surface of the drill string, thereby providing a fluid-tight interface between the stripper rubber and the drill string for containing pressurized drilling substances within the well bore, below the bearing assembly. In this manner, the fluid-tight interface between the stripper rubber and the drill string serves to prevent drilling substances within the well bore from escaping from within the well bore between the inner barrel and the drilling string. The stripper rubber is one example of a sealing device that can be carried by a bearing assembly for the purpose of sealing a drillstring or related piece of drilling equipment extending through the bearing assembly.
As modern wells are drilled ever deeper, or into certain geological formations, very high temperatures and pressures may be imparted upon the drilling substances within the well bore. These rigorous drilling conditions pose significant danger to rig personnel. Examples of such dangers include, but are not limited to being subjected to scalding, burning or contamination by drilling substances such as steam, hot liquids, caustic fluids, and the like. Accordingly, the stripper rubber is replaced periodically to maintain suitable sealing performance at the interface between the sealing device and the drill string.
For similar reasons to why it is imperative to maintain adequate seal between the stripper rubber and the drill string, it is also imperative that a suitable seal be maintained between the bowl and the outer barrel. To this end, a plurality of O-ring seals (i.e., sealing devices) is typically carried on the exterior surface of the outer barrel such that a fluid-tight interface is provided between mating surfaces of the outer barrel and the bowl. These O-ring seals prevent drilling substances from escaping from within the well bore between the mating surfaces of the outer barrel and the bowl. To this end, the O-ring seals can be replaced periodically to maintain suitable sealing performance at the interface between the mating surfaces of the outer barrel and the bowl.
The surface of the bowl that engages the mating surface of the outer barrel can become damaged, thereby preventing the O-ring seals from suitable providing a fluid-tight interface between the mating surfaces of the outer barrel and the bowl. For example, when installing a drill bit into the well bore, the bearing assembly is not yet in place and, thus, the bowl is exposed to contact with the drill bit. As such, contact of the drill bit with the outer barrel engaging surface of the bowl can result in damage to the outer barrel engaging surface of the bowl. If such damage compromises the fluid-tight seal provided by the O-rings of the outer barrel, the damage must be rectified prior to commencing drilling operations. Accordingly, a drawback of prior art bowls with outer barrel engaging surface of the bowl machined directly into the bowl is that the entire bowl typically must be removed from the drilling rig or associated piece of well drilling equipment in order to repair the damaged portion of the outer barrel engaging surface or to replace the bowl. Such removal of the bowl is time consuming, thereby making it an expensive and undesirable undertaking.